The quantitative determination of analytes in body fluids is of great importance in the diagnoses and maintenance of certain physiological abnormalities. For example, lactate, cholesterol, and bilirubin should be monitored in certain individuals. In particular, it is important that diabetic individuals frequently check the glucose level in their body fluids to regulate the glucose intake in their diets. The results of such tests can be used to determine what, if any, insulin or other medication needs to be administered. In one type of blood-glucose testing system, test sensors are used to test a sample of blood.
A test sensor contains biosensing or reagent material that reacts with blood glucose. The testing end of the test sensor is adapted to be placed into the fluid being tested, for example, blood that has accumulated on a person's finger after the finger has been pricked. The fluid is drawn into a capillary channel that extends in the test sensor from the testing end to the reagent material by capillary action so that a sufficient amount of fluid to be tested is drawn into the test sensor. Alternatively, the person could apply a drop of blood to the test sensor that incorporates a reactive zone containing biosensing or reagent material capable of reacting with blood glucose. A voltage is applied, causing the fluid to then chemically react with the reagent material in the test sensor, resulting in an electrical signal indicative of the glucose level in the fluid being tested. This signal is supplied to a sensor-dispensing instrument, or meter, via contact areas located near the rear or contact end of the test sensor and becomes the measured output.
A problem occurs when the test sensor is modified, such as, for example, modifying the reagent material. Modified test sensors are typically newer test sensor versions with improved features, such as improved performance or shortened test times. The modified test sensors may require the meter to apply different calibration information and testing sequences when testing a sample. During the time period before the modified test sensor is to be launched, there exists significant inventory of existing test sensors. Thus, it is desirable that different versions of test sensors may be used interchangeably in a single instrument or meter. Accordingly, the meter should be capable of distinguishing between the various versions of test sensors so that the proper calibration information and testing sequences are applied, and an accurate analyte reading is obtained.
Existing methods for differentiating between different test sensors versions include requiring a user to perform an affirmative act, such as changing a code chip or pressing a button on the meter, to signal to the meter that the test strip is a newer version requiring the application of different calibration information and/or testing sequences. The requirement that a user perform an affirmative act to signal to the meter which type of test sensor is being used allows for the possibility of human error that can adversely affect the analysis of the test results.
It would be desirable to provide a method for distinguishing between multiple versions of an electrochemical test sensor that would minimize or eliminate the user's involvement.